1,721,120 research outputs found
Lab-scale monitoring of electrokinetic remediation of contaminated sediments
No full textThe management of dredged sediment is commonly recognized as a complex procedure in industrialized countries, where sediments are often contaminated by metals and organic contaminants due to the presence of a number of point and diffuse contamination sources. Due to the huge amounts of sediments to be dredged due for either maintenance or environmental dredging purposes, management options different from landfilling are claimed. Among the available treatment options, Electrokinetic Remediation (EKR) appears to be particularly suitable due to a number of potential advantages, including the capability of treating finely graded and low-permeability matrices such as sediments, and the ability of removing organic and inorganic contaminants. In order to improve the remediation process, enhancing agents such acids, chelating agents, surfactants can be added in the electrode compartments. However, due to the complexity of both the sediment matrix and the contaminants nature, despite the interest demonstrated by the scientific sector in EK, the uncertainties in process yields and control still hinder its full-scale application. This work was aimed at studying EKR for metal removal from contaminated sediment samples from three Italian harbors. The lab-scale EKR tests were performed using different types of acids, namely acetic, nitric and hydrochloric aci
Opportunities for the use of agroindustrial organic residues in biorefineries
No full textIn order to reduce the amount of landfilled waste and to attain the valorization of the material and energy content of organic wastes, the integrated approach based on the biorefinery concept seems to be the most promising in terms of resource recovery, technical feasibility as well as overall environmental and economic benefits. Biorefineries are aimed at converting biomass into biofuels and biobased products, thus they can contribute to reducing the overall consumption of fossil fuels and to minimizing the global carbon footprint of both energy and material production. Compared to conventional refineries, the “bio” configuration allows for producing gaseous/ liquid fuels, plastics and valuable compounds starting from organic biomass instead of hydrocarbons, and may consequently contribute to the reduction of the global carbon footprint and dependency on fossil fuels. Irrespectively of the specific outputs, microbial fermentation, possibly controlled so as to increase the process yields and the products quality, represents the core process in the biorefinery concept. As for the biomass to be treated, an intense debate has grown over the utilization of food crops for biofuels and biomaterials production since the end of 1900, when the opponents stated that such a practice involve turning food for the poor into fuel for the rich, worsen soil erosion and may result into marginal replacement of fossil fuels. A strategy to overcome the food vs. fuel dilemma might be represented by the utilization of residual biomass, such as the biodegradable fraction of municipal waste and agro-industrial residues, as a feedstock for biorefineries. The present paper presents an overview of the most interesting metabolic pathways for liquid and gaseous biofuels. Conceptual schemes for integrating different fermentation processes aimed at biofuels and bioplastics production will be also shown
Parametric analysis of fermentative hydrogen production from cheese whey
No full textCheese whey (CW) is one of the most abundant by-products of cheese manufacturing, as about 9.0 kg of CW are generated for each kg of cheese produced. Due to its origin, it is a high strength wastewater characterized by high chemical and biochemical oxygen demand. Thus, identification of proper strategies for CW management is a challenging topic in view of reducing both treatment cost and environmental impacts. Among the different options, anaerobic digestion can be regarded as one of the most promising, being able to reduce the organic load of CW while harversting its energy content. Recently, an increasing attention has been paid to dark fermentation of CW, as according to theoretical calculations, 8 mol H2 can be produced per mole of degraded lactose in quite short digestion time. H2 may be used as fuel or in fuel cells, whilst the effluent may be fed to a second-stage conventional anaerobic digester for CH4 production.
In the present study, the effect of pH conditions and inoculum addition on H2 production from CW was investigated under continuously stirred batch conditions by designing the experiments according to the principles of a factorial design. According to this approach, the set-point of the pH values of the system and the amount of inoculum added to CW was varied over four values. As inoculum, the aerobic sludge from a wastewater treatment plant was used, after heat-shocking at 110°C for 30 minutes so as to harvest the hydrogenogenic biomass. Process performance was evaluated in terms of H2 production and substrate conversion efficiency, by three process indicators: 1) amount and composition of the produced biogas evolution of the metabolic pathways, 2) evolution of substrate degradation, expressed as the removal total organic carbon (TOC) and carbohydrates
Influence of particle size on the carbonation of stainless steel slag for CO2 storage
No full textAbstractThe main aims of this work were to assess the CO2 storage capacity of different particle size fractions of stainless steel slag subjected to accelerated carbonation under mild operating conditions, to study the influence on reaction kinetics of some of the main operating parameters (temperature, pressure and liquid to solid ratio) and to determine the effects of the process on slag mineralogy and leaching behavior. Maximum CO2 uptakes of 130 g CO2/kg residues were measured for the finest grain size and decreased with particle size owing to differences in reacting species availability and specific surface. Process kinetics proved relatively fast, achieving completion in around 2 hours with a CO2 pressure of 3 bar and an optimal liquid to solid ratio of 0.4; temperature was the parameter that most influenced CO2 uptake, due to its enhancement effect on silicates dissolution
La produzione di H2 e CH4 mediante digestione anaerobica di fanghi dal trattamento di reflui civili, agroindustriali e zootecnici
No full textA review of dark fermentative hydrogen production from biodegradable municipal waste fractions
No full textIn view of the implementation of a sustainable energy conversion framework, hydrogen is believed to potentially play a key role, significantly contributing to the reduction of the associated environmental impacts. Although H2 can be obtained from different sources through a variety of processes, positive environmental implications are specifically envisaged when H2 production is attained from renewable sources and low energy-demanding processes. H2 generation through dark fermentation of biodegradable organic residues has for such reasons deserved considerable attention over the last few decades. The main technical issue to be addressed is deemed to involve achieving efficient H2 generation at reasonably low costs at the same time gaining environmental credits. The great deal of scientific work on this issue as well as the large number of factors affecting fermentative hydrogen production claim for a harmonization and systematic comparison of results from different literature sources in order to derive reliable information about process yield and stability, and build related predictive models. To this aim, a review was conducted of studies on hydrogen production from kitchen waste (KW) and organic fractions of municipal solid waste (OFMSW) through dark fermentation, with more than 80 recent related publications being examined. The analysis focused on the effect of several factors, recognized as potentially affecting process evolution (including type of substrate and co-substrate and relative ratio, type of inoculum, food/microorganisms [F/M] ratio, applied pre-treatment, reactor configuration, temperature and pH), on the fermentation yield and kinetics. Experimental hydrogen production data from the reviewed literature were analyzed using statistical tools to derive information on the relative importance of the main variables of relevance also identifying existing mutual relationship
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